High-density optical fiber ribbon interconnect and method of making

ABSTRACT

A fiber ribbon interconnect may include a fiber ribbon, a first optical connector at a first end of the fiber ribbon, and a second optical connector at a second end of the fiber ribbon. The fiber ribbon includes two or more cladding-strengthened glass optical fibers each having an outer surface. The fiber ribbon also includes a common protective coating that surrounds the outer surfaces of the two or more cladding-strengthened glass optical fibers.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.16/689,144, filed on Nov. 20, 2019, which claims the benefit of priorityof U.S. Provisional Application No. 62/778,593, filed on Dec. 12, 2018,both applications being incorporated herein by reference.

FIELD

The present disclosure relates to optical fiber ribbon interconnects,and in particular to a high-density optical fiber ribbon interconnectwith a fiber ribbon having cladding-strengthened glass optical fibers ina common protective coating.

BACKGROUND

The push for higher data rates in digital communications has driven theintegration of optics with electronics. In particular, the use ofsilicon photonics for electro-optical transceivers has resulted in verydense optical circuitry concentrating many separate optical signal linesin the form of optical waveguides (e.g., channel waveguides) into onesilicon photonics chip. For many optical signal transmissionapplications, the optical signals generated on the silicon photonicschips need to be coupled from the optical waveguides into opticalfibers. Likewise, optical signals generated at a remote location (e.g.,a telecommunications device) need to be coupled from optical fibers tothe optical waveguides to be detected by the silicon photonics chip.

Optical fiber ribbons and multicore optical fibers are two approaches toincrease the fiber density to achieve the parallel connectivity requiredfor the optical circuitry of silicon photonics chips. Unfortunately,using conventional optical fibers in a fiber ribbon does not result in asufficiently high fiber density due to their relatively large size (asdefined by the core, cladding and protective coating) as compared to thesize of the optical waveguides of the silicon photonics chips. Likewise,the use of multicore optical fibers is problematic due to manufacturingshortcomings (e.g., maintaining concentricity of the hard protectivecoating), the high connectivity costs, and the lack of componentecosystems.

SUMMARY

A high-density fiber ribbon interconnect includes an optical fiberribbon and at least one connector. The optical fiber ribbon includes twoor more cladding-strengthened glass optical fibers each having an outersurface and each not individually including a protective polymercoating. A protective polymer coating substantially surrounds the outersurfaces of the two or more cladding-strengthened glass optical fibersso that the protective polymer coating is common to the two or morecladding-strengthened glass optical fibers. A fiber ribbon cable isformed by adding a cover assembly to the fiber ribbon. A fiber ribboninterconnect is formed by adding one or more optical connectors to thefiber ribbon or fiber ribbon cable. Optical data transmission systemsthat employ the fiber ribbon to optically connect to a photonic deviceare also disclosed.

Present day optical transceivers used on silicon photonics chips ofphotonic devices operate at a speed of 100 Gb/s based on 4 lanes at 25Gb/s per lane. The roadmap for electrical lane speed has been definedfor the next generation, and the existing 25 Gb/s lane speed willincrease to 56 GBaut/s in the PAM4 signaling protocol which amounts to112 Gb/s per lane (PAM stands for “pulse amplitude modulation”). The 400Gb/s Ethernet speed will therefore continue to follow the 4-lanearchitecture. The optics to support 4 electrical lanes are currentlybased on either PSM4 (parallel single mode 4 fibers) or the CWDM4signaling protocol (i.e., 4 wavelength coarse wavelength divisionmultiplexing). The transceiver optical interface is typically an 8 fiberMPO for PSM-4, and a duplex LC for CWDM4.

The pro and cons of the PSM4 versus CWDM4 signaling protocols has beenan ongoing debate. The PSM4 transceiver that employs a standard ribbonfiber is currently the lower cost solution, even though the connectivitycost is considerably higher than CWDM4 due to the use of a manualpush-on pull-off (MPO) connector. The PSM4 protocol consumes more chipspace for coupling to fibers. On the other hand, the CWDM4 transceiverssuffer from the excess insertion loss of the WDM multiplexer andde-multiplexer, which typically exceeds 4 decibels (dB). As thetransceiver speed increases, the link budget will be challenged toaccommodate the high insertion loss of WDM components. Moreover, CWDMtransceivers require multiple laser sources and consume more power thanPSM4 transceivers. As mega data centers increasingly focus on energyefficiency, parallel single mode remains an appealing solution if theconnectivity density can be improved.

The fiber ribbons, cables and assemblies disclosed herein substantiallyenhance the density of parallel fiber connectivity with photonic devicesthat include silicon photonics chips (e.g., transceiver chips thatsupport optical waveguides) without resorting to the use of multicorefibers. The conventional approach to improving the fiber density in anoptical fiber-based connection has been to reduce the thickness of theprotective coating(s) of the optical fibers. A 200 μm diameter fiber,for instance, is designed to reduce the protective coating thicknessfrom 250 μm while using the same glass cladding diameter of 125 μm. Theimprovement in fiber density has been appreciable for high-fiber-countcables when protective coating thickness is reduced. For transceiverchip coupling, however, the density improvement is incremental at best.

In an example, the high-density fiber ribbons disclosed herein comprisea closely packed array of single-mode fibers in one or more rows, witheach fiber having a strengthened cladding and a single common protectivecoating that directly encapsulates all the fibers, with the exception ofthe fiber ends as well as the fiber end sections in some examples. Eachfiber is made entirely of glass and does not have an individualnon-glass protective coating, other than perhaps a thin hermetic sealcoating. The lack of individual protective coatings allows formaximizing the fiber density in a fiber ribbon configuration withoutcompromising the optical transmission properties of the fibers.

The fiber cladding is made of silica and includes an inner cladding andan outer cladding. The outer cladding is compositionally distinct fromthe inner cladding and has higher mechanical strength, greater abrasionresistance, and/or greater fatigue resistance than the inner cladding.The outer cladding is referred to herein as a “strengthened cladding” ora “strengthened outer cladding” and a fiber having the outer cladding isreferred to herein as a “cladding-strengthened fiber” or a“cladding-strengthened optical fiber” or a “cladding-strengthened glassoptical fiber”. The outer cladding is strengthened by doping silicaglass. In one aspect, a strengthened outer cladding is made by dopingsilica glass with titanium dioxide (TiO₂). Doping of silica glass toform a strengthened outer cladding improves the scratch and fatigueresistance of the fiber and permits handling and installation of thefiber (e.g. in a ribbon) without damage. The strengthened outer claddingis sufficiently robust to obviate the need for an individual protectivecoating for each fiber in a ribbon. The overall fiber diameter isaccordingly reduced and a higher packing density of fibers in a ribbonis achieved.

The common protective coating can be based on an ultraviolet (UV)curable acrylate, a thermoplastic, or other adhesives. The collectivelycoated fiber array can include indicia (i.e., features, shapes,markings, etc.) to identify the polarity of the fiber ribbon. The pitchof the fiber array of the fiber ribbon can be transitioned from arelatively high fiber density (e.g., substantially equal to the fiberdiameter) at one end to up to 250 μm at the other end. In an example,this can be accomplished using a fan-out structure configured tominimize bending. The different fiber densities can be exploited formass fusion splicing or termination by MPO ferrules for subsequenttermination by an MPO connector. The fiber ribbon can be made compatibleto standard 127 μm pitch grooves of a grooved substrate, enabling asimple assembly process for high-density connector assemblies, such asfiber array units (FAUs).

The fiber array can be collectively coated into a relatively small formfactor. With a standard outer cladding diameter of 125 μm, thehigh-density fiber array can utilize existing fiber terminationequipment and connectivity components. Higher fiber densities can beachieved by reducing the outer cladding diameter to 80 μm or even lower.Without protective coatings on the individual fibers, the tightly packedfiber array has inherent geometric precision due to the highmanufacturing tolerance and consistency of the fiber outer claddingdiameter associated with the fiber drawing process.

The present disclosure extends to a fiber ribbon interconnect thatincludes a fiber ribbon, a first optical connector at a first end of thefiber ribbon and a second optical connector at a second end of the fiberribbon. The fiber ribbon includes two or more cladding-strengthenedglass optical fibers each having an outer surface and a commonprotective coating that substantially surrounds the outer surfaces ofthe two or more cladding-strengthened glass optical fibers.

The present disclosure also extends to a fiber ribbon interconnect thatincludes a fiber ribbon and a first optical connector at a first end ofthe fiber ribbon. The fiber ribbon includes two or more glass opticalfibers each having an outer surface, wherein the two or more glassoptical fibers do not include individual protective coatings. The fiberribbon also includes a common protective coating that surrounds theouter surfaces of the two or more glass optical fibers.

The present disclosure also extends to a fiber ribbon interconnect thatincludes a high-density optical fiber ribbon having a first end sectionwith a first end, and at least one second end section with at least onesecond end. The fiber ribbon also includes two or more glass opticalfibers arranged in at least one row, with each of the two or more glassoptical fibers having an outer surface and not having an individualprotective coating. The fiber ribbon also includes a common protectivecoating that substantially surrounds the outer surfaces of the two ormore glass optical fibers. The fiber ribbon interconnect also includes ahigh-density optical fiber connector connected to the first end of thehigh-density optical fiber ribbon.

The present disclosure also extends to a method for making a fiberribbon interconnect. The method includes forming a protective polymercoating surrounding outer surfaces of two or more glass optical fibers,wherein the two or more glass optical fibers do not include individualprotective coatings, and wherein the protective polymer coating iscommon to the two or more glass optical fibers to define an opticalfiber ribbon having first and second ends. The method also includescoupling a first optical connector to the first end of the optical fiberribbon.

Additional features and advantages are set forth in the DetailedDescription that follows, and in part will be apparent to those skilledin the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings. It is to be understood that both theforegoing general description and the following Detailed Description aremerely exemplary, and are intended to provide an overview or frameworkto understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the Detailed Description explain the principles andoperation of the various embodiments. As such, the disclosure willbecome more fully understood from the following Detailed Description,taken in conjunction with the accompanying Figures, in which:

FIG. 1 is a front elevated view of an example cladding-strengthenedglass optical fiber as disclosed herein.

FIG. 2A is a cross-sectional view of the cladding-strengthened glassoptical fiber of FIG. 1.

FIG. 2B is similar to FIG. 2A, but shows an embodiment of thecladding-strengthened glass optical fiber that includes a hermeticsealing layer.

FIG. 3A is a schematic diagram of an optical fiber drawing system usedto form the cladding-strengthened glass optical fibers disclosed herein.

FIGS. 3B and 3C are close-up views of the glass outer surface of thecladding-strengthened glass optical fiber and illustrate how the outersurface can be readily functionalized using a fluourinated silane.

FIG. 3D is a plot of the contact angle θ (°) versus measurement positionP (mm) for a bare fiber (10B) and for a fiber (10) having a silane-basedhermetic sealing layer.

FIG. 4A is a top-down view of an example fiber ribbon that employs thecladding-strengthened glass optical fibers embedded in a commonprotective coating.

FIG. 4B is a cross-sectional view of the fiber ribbon of FIG. 4A.

FIG. 4C is similar to FIG. 4B and shows two rows of thecladding-strengthened glass optical fibers within the common protectivecoating.

FIG. 4D is a close-up cross-sectional view of a portion of the fiberribbon of FIGS. 4A and 4B, illustrating an example where the commonprotective coating comprises two different materials that define aprimary (inner) layer and a secondary (outer) layer.

FIG. 4E is similar to FIG. 4B and shows an example where the commonprotective coating is thicker on one side of the cladding-strengthenedglass optical fibers than the other as an indication of the polarity ofthe fiber ribbon.

FIG. 5A is a top down view of an example fiber ribbon cable formed usingthe fiber ribbon.

FIGS. 5B through 5D are cross-sectional views of the fiber ribbon cableof FIG. 5A, wherein the fiber ribbon cable comprises the fiber ribbonand a cover assembly that surrounds the outside of the fiber ribbon.

FIG. 6 is an elevated view of an example fiber ribbon interconnect thatcomprises the fiber ribbon cable connectorized at its opposite ends withoptical fiber connectors.

FIG. 7A is an exploded front elevated view of an example method offorming a high-density connector assembly that can be used directly as ahigh-density optical fiber connector or that can be used to form ahigh-density optical fiber connector.

FIG. 7B is a front elevated view of the assembled high-density connectorassembly.

FIG. 7C is a cross-sectional view of the high-density connector assemblyof FIG. 7B, illustrating an example of the cladding-strengthened glassoptical fibers extracted from the protective coating of the fiberribbon, and the fiber ribbon extracted from the cover assembly.

FIG. 7D is an elevated view illustrating how the high-density connectorassembly of FIG. 7B can be used to form a high-density optical fiberconnector by adding additional components in the form of a connectorhousing and alignment features.

FIG. 8A is a top-down view of an example fan-out fiber ribbon.

FIGS. 8B and 8C are x-y cross-sectional views of the fan-out fiberribbon of FIG. 8A taken at the lines B-B and C-C respectively, andillustrating how the fiber pitch (density) can be made different at theopposite ends of the fan-out fiber ribbon using a fan-out region.

FIG. 9 is a top-down view of an example fiber ribbon interconnect thatcomprises the fan-out fiber ribbon of FIG. 8A with a high-densityoptical fiber connector operably attached to the high-density (narrow)end and a conventional (e.g., MPO) connector attached to thestandard-density (wide) end.

FIG. 10A is an elevated view of an example furcated fiber ribbon.

FIG. 10B is a cross-sectional view of each of the furcations of thefurcated fiber ribbon of FIG. 10A.

FIG. 10C is similar to FIG. 10A and shows an example interconnect thatemploys the furcated fiber ribbon.

FIG. 11A is as schematic diagram of an optical data transmission systemthat employs the fiber ribbon as disclosed herein.

FIG. 11B is a close-up view of one end of the fiber ribbon connectorizedwith a high-density optical fiber connector, which is in position tooperably engage a photonics chip of a photonic device.

FIG. 11C is similar to FIG. 11B and shows the high-density optical fiberconnector operably engaged with the photonics chip of the photonicdevice so that the cladding-strengthened glass optical fibers are inoptical communication with optical waveguides supported by the photonicschip.

FIG. 11D is a side view of a connectorized end of an example fiberribbon interconnect, wherein the connectorized end includes a standardconnector, and illustrating an example of how the fiber ribboninterconnect can be optically connected to a standard optical fibercable using an adapter.

FIG. 11E is a top-down view of an example of an optical datatransmission system wherein a fiber ribbon interconnect terminated bytwo high-density optical connectors is used to optically connect twodifferent photonic devices.

FIG. 11F is similar to FIG. 11E and shows an example of an optical datatransmission system wherein the fiber ribbon interconnect utilizes abifurcated fiber ribbon to provide high-density optical interconnectionsbetween one photonic device at one end of the fiber ribbon interconnectand two photonic devices at the other end of the fiber ribboninterconnect.

DETAILED DESCRIPTION

Reference is now made in detail to various embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Whenever possible, the same or like reference numbers andsymbols are used throughout the drawings to refer to the same or likeparts. The drawings are not necessarily to scale, and one skilled in theart will recognize where the drawings have been simplified to illustratethe key aspects of the disclosure.

The claims as set forth below are incorporated into and constitute partof this Detailed Description.

Cartesian coordinates are shown in some of the Figures for the sake ofreference and are not intended to be limiting as to direction ororientation.

The expression “comprises” as used herein includes the term “consistsof” as a special case, so that for example the expression “A comprises Band C” is understood to include the case of “A consists of B and C.”

Relative terms like top, bottom, side, horizontal, vertical, etc. areused for convenience and ease of explanation and are not intended to belimiting as to direction or orientation.

The acronym MPO as used herein stands for multifiber push on and is usedto describe a type of optical fiber connector known in the art and thatis standard in the art.

The term “elastic modulus” as used herein refers to Young's modulus.

The terms “optical fiber” and “glass optical fiber” as used herein referto a glass fiber configured to operate as a waveguide.

Fiber with Strengthened Cladding

FIG. 1 is a front elevated view of an example cladding-strengthenedglass optical fiber (“fiber”) 10 as disclosed herein. FIG. 2A is across-sectional view of the fiber 10 of FIG. 1. The fiber 10 has acenterline AC, a core 16 centered on the centerline and having adiameter D1, and a cladding 20 surrounding the core and having adiameter D2 and a thickness TH2. The core 16 and cladding 20 are bothmade of glass and can have the configuration (i.e., refractive indexprofile, dimensions, etc.) of a conventional optical fiber. Therefractive index profile of the fiber 10 can be that for a standardsingle mode fiber, a bend-insensitive single mode fiber, a few-modefiber, or a multimode fiber.

An example diameter D1 of the core 16 for a single mode fiber is in therange from about 5 microns to about 10 microns, with about 8 micronsbeing typical value for telecommunications wavelengths of 1310 nm and1550 nm. An example diameter D2 of the cladding 20 is in the range fromabout 30 μm to about 250 μm, depending on the desired overall fiberdiameter DF, which in an example can be in the range from 50 μm to 200μm.

The fiber 10 also includes an additional cladding 30 that surrounds thecladding 20, so that the cladding 20 can be considered an inner claddingand the cladding 30 considered an outer cladding of a two-part claddingregion 40. The outer cladding 30 has a diameter D3 and a thickness TH3.An example range on the thickness TH3 is between 1 μm and 20 μm.

The outer cladding 30 comprises silica (SiO₂) doped with titaniumdioxide (TiO₂, which is also called “titania”). An example of such afiber 10 is the Corning® Titan® single-mode optical fiber, availablefrom Corning, Inc., Corning, N.Y. The outer cladding 30 strengthens thefiber 10 and in particular provides abrasion and/or fatigue resistanceto the fiber 10. That is, outer cladding 30 has a higher strengthparameter S and/or a higher dynamic fatigue parameter nd than innercladding 20. A fiber with a strengthened outer cladding 30 is referredto herein as a “cladding-strengthened fiber”, or a“cladding-strengthened optical fiber”, or a “cladding-strengthened glassfiber”, or a “cladding-strengthened glass optical fiber”. The outercladding 30 need not be stripped off during splicing or termination. Theouter cladding 30 has an outer surface 32, which defines the outersurface of the cladding region 40. The outer surface 32 is a glasssurface.

The outer cladding 30 has an amount of compressive stress SC thatstrengthens the outer surface 32 of the outer cladding layer in a mannersimilar to chemically strengthened glasses. In an example, the amount ofcompressive stress SC is in the range from 30 MPa to 100 MPa. Inaddition, the formation of microcrystals due to doping of the SiO₂ withtitania can stop defects such as scratches from propagating through thefiber 10, resulting in further fatigue resistance. In an example, thedoping concentration of titania in the SiO₂ of the outer cladding 30 isin the range from 5 wt % to 25 wt %. The outer cladding 30 contributesto the overall refractive index profile of the fiber 10, but is alsodesigned to avoid excess loss of the guided light from the core 16.Because the titania dopant in silica glass increases the refractiveindex, it can cause tunneling loss of guided light traveling in the core16 to the titania doped outer cladding 30. To avoid this excess loss,the starting position (inner radius) of outer cladding 30 needs to besufficiently away from the core. Preferably, the spacing (radialdistance) between the core 16 and the outer cladding 30 (i.e., thethickness TH2 of the inner cladding 20 as shown in FIG. 2A) is greaterthan 25 μm and more preferably greater than 30 μm.

The fiber 10 also has an outer surface 70. In the example of FIG. 2A,fiber 10 is bare fiber 10B and outer surface 70 is the same as the outersurface 32 of the outer cladding 30. FIG. 2B is similar to FIG. 2A andillustrates an example sealed fiber 10H that includes a hermetic sealinglayer 50 on the outer surface 32 of the outer cladding 30. In anexample, the hermetic sealing layer 50 comprises or consists essentiallyof carbon. In one example, the hermetic sealing layer 50 has a thicknessTH5<100 nm and so does not contribute substantially to the overall size(diameter DF) of the sealed fiber 10H. In an example, the hermeticsealing layer is made of an inorganic material, e.g., is not made of anorganic polymer such as acrylate. The hermetic sealing layer 50 isdesigned to prevent moisture and other adverse materials in theenvironment from entering and possibly damaging the fiber. The hermeticsealing layer 50 is thus substantially different in chemical compositionfrom a protective coating used on conventional individual optical fibersor the common protective coating for fibers in an array or bundle.Protective coatings for individual optical fibers and fiber arrays orbundles are organic polymers. The organic polymers are formed bypolymerizing organic monomers, usually acrylate or methacrylatemonomers.

Thermoplastic organic polymers are also used as protective coatings forindividual optical fibers and fiber arrays or bundles. The hermeticsealing layer 50 is not an organic polymer and has a thickness wellbelow the thickness used for the protective coatings of individualoptical fibers or fiber arrays or bundles. In an example discussedbelow, the hermetic sealing layer comprises a self-assembled monolayer(SAM), such as formed using a silane compound. Example hermetic sealinglayers 50 are discussed in greater detail below. In the discussionsbelow, the fiber 10 can be a fiber such as sealed fiber 10H in FIG. 2Bor a bare fiber 10B such as in FIG. 2A, unless the particular type offiber is specified.

A given length of fiber 10 has opposite end sections 60 each with an endface 62, as shown in FIG. 1. The fiber 10 has the aforementioned outersurface 70, which can be defined by the cladding region 40 as in barefiber 10B of FIG. 2A or the hermetic sealing layer 50 as in sealed fiber10H of FIG. 2B, depending on the configuration of the fiber.

In the discussion and in the drawings, reference to fiber 10 refers toeither bare fiber 10B or the sealed fiber 10H, unless otherwise noted.

Fabricating the Fiber

The fiber 10 can be made by drawing a fiber from a preform usingstandard optical fiber fabrication drawing techniques. FIG. 3A is aschematic diagram of an example optical fiber drawing system (“drawingsystem”) 100. The drawing system 100 may comprise a draw furnace 102 forheating the preform to the glass melt temperature, non-contactmeasurement sensors 104A and 104B for measuring the size of the drawnfiber as it exits the draw furnace for size (diameter) control, acooling station 106 to cool the drawn fiber, a tensioner 120 with asurface 122 to pull (draw) the fiber, guide wheels 130 with respectivesurfaces 132 to guide the drawn fiber, and a fiber take-up spool(“spool”) 150 to store the drawn fiber.

The drawing system 100 also includes a preform holder 160 locatedadjacent the top side of the draw furnace 102 and that holds a glasspreform 10P used to form the fiber 10. With reference to the close-upinset of FIG. 3A that shows a cross-sectional view of the glass preform10P, the preform has a preform core 16P, an inner preform cladding 20Pand a outer preform cladding 30P. The glass preform 10P has generallythe same relative configuration and dimensional proportions in theradial direction as bare fiber 10B but is much larger, e.g., 25X to 100Xlarger.

The preform core 16P can be made by doping silica with anindex-increasing dopant such germanium oxide. The inner preform cladding20P and outer preform cladding 30P start out as pure silica (SiO₂). Thepreform outer cladding 30P is then doped with titania to strengthen it.The glass preform 10P and in particular preform core 16P and the innerpreform and outer preform cladding layers 20P and 30P may be produced ina single-step process or multi-step process. Suitable methods orprocesses include: the double crucible method, rod-in-tube procedures,and doped deposited silica processes, also commonly referred to aschemical vapor deposition (CVD). A variety of CVD processes are knownand are suitable for producing the core and cladding layers used in theoptical fibers of the present invention. They include outside vapordeposition process (OVD) process, vapor axial deposition (VAD) process,modified CVD (MCVD), and plasma-enhanced CVD (PECVD).

After the glass preform 10P is formed, it is operably supported in thepreform holder 160 relative to the draw furnace as shown in FIG. 3A. Theglass preform 10P is then heated by the draw furnace 102 and drawn intofiber 10 using the drawing system 100. The drawing process is similar toa conventional fiber draw process, except that no polymer coatings areadded to the fiber 10, i.e. the fiber is a bare glass fiber 10B with astrengthened outer cladding 30 or a sealed glass fiber 10H with astrengthened outer cladding 30 and a hermetic sealing layer 50 asdiscussed above. Note in particular that the doped outer preformcladding 30P defines the chemically strengthened (doped) outer cladding30 when the preform 10P is drawn to form the fiber 10.

In the fabrication process, the fiber drawn from glass preform 10P exitsthe draw furnace 102, with tension applied by the tensioner 120. Thedimensions (e.g., the diameter) of the fiber are measured by thenon-contact sensors 104A and 104B and the measured dimensions are usedto control the draw process. The fiber can then pass through the coolingmechanism 106, which can be filled with a gas that facilitates coolingat a rate slower than air at ambient temperatures. At this point, thefiber 10 is a bare fiber 10B.

The fiber 10 passes from the tensioner 120 to the guide wheels 130, thenthrough the guide wheels to the spool 150, where the fiber 10 is takenup and stored. It is noted that a bare glass fiber without a protectivecoating that lacks outer cladding 30 cannot be collected on a take-upspool as a practical matter due to the high break rate due to surfacedamage to the fiber. The strengthened outer cladding 30 of fiber 10makes possible collecting this glass fiber on the spool 150 withoutbreaks. Also, in an example, the tensioner surface 122 and the guidewheel surfaces 132 preferably comprise either a polymer material such asa fluoropolymer (e.g., polytetrafluoroethylene or PTFE), or a plasticmaterial or a rubber material, to protect the fiber 10 from surfacedamage.

The configuration of the glass preform 10P and the various drawingparameters (draw speed, temperature, tension, cooling rate, etc.)dictate the final form of the fiber 10.

Embodiments of the Hermetic Sealing Layer

In the example sealed fiber 10H of FIG. 2B that includes the hermeticsealing layer 50 (i.e., the coated fiber), the drawing system 100 caninclude an applicator device 170 that applies a hermetic sealing layermaterial 50M to the drawn bare fiber 10B as the bare fiber 10B passes bythe applicator device 170. The applicator device 170 can also be onethat is off-line, i.e., in another location besides in the drawingsystem 100 and employed after the bare fiber 10B is collected on thespool 150, with the fiber distributed from the spool for application ofthe hermetic sealing layer material 50M to bare fiber 10B by theapplicator device 170 for form hermetic sealing layer 50.

In an example, the hermetic sealing layer material 50M comprises aninorganic material, such as an inorganic hydrophobic material. Hermeticsealing layer materials that include silicon are regarded herein asinorganic materials even if carbon or an organic fragment is bonded tosilicon. Organosilanes, for example, are regarded as inorganic materialsfor purposes of the present disclosure.

In another example, the hermetic sealing layer material 50M comprises aself-assembled monolayer (SAM). In an example, the SAM is formed using asilane, preferably an organosilane, which can be applied in liquid formonto the bare fiber 10B using the applicator device 170. The SAMhermetic sealing layer material 50M that defines an example hermeticsealing layer 50 produces a hydrophobic outer surface 70 for the sealedfiber 10H that shields the outer cladding 30 from moisture, therebyslowing down the development of glass fatigue and reduce fiber breaks.Because the SAM layer is thin (e.g., <10 nm), it does not need to beremoved when making the fiber ribbon (introduced and discussed below),and does not affect fiber positioning (e.g., the fiber ribbon pitch). Insome embodiments, the SAM layer covers or is uniformly distributed overthe entirety of the outer surface 32 of the outer cladding 30. In otherembodiments, the SAM layer does not cover or is not uniformlydistributed over the entirety of the outer surface 32 of the outercladding 30. For example, gaps may exist in the SAM layer and portionsof the outer surface 32 of the outer cladding 30 may be exposed.

One example of a silane in liquid form comprises octadecyldimethyltrimethoxysilylpropyl ammonium chloride (60 wt % in MeOH), acetic acid(0.05 wt %) and deionized water (18 Mohm, 0.2 micron filtered). In anexample, the proportions by weight of the three ingredients can be16.7:1:19823.4. The deposited layer of the silane liquid as the hermeticsealing layer material 50M produces on the outer surface 32 of the outercladding 30 a hermetic sealing layer 50 with a hydrophobic fiber outersurface 70 that can inhibit moisture from getting into the glassmaterial of the fiber.

FIGS. 3B and 3C are close-up views of the outer surface 32 of the sealedfiber 10H and illustrate how the outer surface can be functionalizedusing a fluourinated silane 80 as hermetic sealing material 50M. Thefluorinated silane 80 includes a silane core 82 and fluorinated chain 84attached thereto. The fluorinated silane 80 can be can be introduced tothe outer surface 32 (FIG. 3B) so that the silane core 82 bonds tosilanol groups 86 on the outer surface 32, thereby forming the thinsilane-based SAM hermetic sealing layer 50 (FIG. 3C).

In an example, a solution of perfluoropolyether-functionalized silane 80was used as the hermetic sealing layer material 50M to create ahydrophobic hermetic sealing layer 50. The silane-based hermetic sealinglayer material 50M was prepared as a solution by adding 0.12 vol %perfluoropolyether-functionalized silane to a fluorinated solvent. Asilane-based hermetic sealing layer material 50M can be applied to thebare fiber 10B by using an applicator device 170 that includes a diecontaining the liquid hermetic sealing layer material 50M. After passingthrough the die, a thin layer of the hermetic sealing layer material 50Mis coated on the outer surface 32. Some hermetic sealing layer materials50M can be dried in air at the ambient temperature. Some hermeticsealing layer materials 50M require curing. The curing can be done byheating for heat-curable materials or by UV light for UV-curablematerials.

In another example, the hermetic sealing layer material 50M comprisescarbon to define a carbon-based hermetic sealing layer 50. The carboncan be deposited on the outer surface 32 of the outer cladding 30 by theapplicator device 170 in the form of an atmospheric chemical vapordeposition chamber in which a hydrocarbon gas, such as methane,acetylene, ethylene, propane, etc. undergoes pyrolysis and aheterogeneous reaction on the outer surface 32. Carbon is stronglybonded to silica with Si—C bond. The carbon layer has typically arandomly oriented graphite platelet structure or amorphous cross-linkedgraphite structure. Forms of carbon with graphite structures areregarded herein as inorganic materials.

The wettability of example sealed fibers 10H with the hermetic sealinglayer 50 was evaluated by using dynamic contact angle measurement usinga tensiometer (K100C-MK2, Kruss GmbH, Germany). The contact angle θ is aquantitative measure of wettability of the outer surface 70 of the fiber10H by a liquid. Generally, if the contact angle θ is less than 90° thesurface is said to be hydrophilic. On the other hand, if the contactangle θ is greater than 90°, the surface is said to be hydrophobic.

FIG. 3D is a plot of the contact angle θ (°) versus measurement positionP (mm) for a bare fiber 10B (i.e., no hermetic sealing layer 50; seeFIG. 2A) and for a sealed fiber 10H (see FIG. 2B) having a silane-basedhermetic sealing layer 50 as described above. The plot includes theadvancing contact angle measured as the sample fiber 10 is immersed inthe liquid (+P direction) and the receding contact angle measured as thesample fiber emerges from liquid (−P direction). Table 1 below lists theadvancing, receding and the contact angle hysteresis (difference betweenthe advancing and receding contact angle). The contact angle hysteresisis a measure of surface heterogeneity and surface roughness.

TABLE 1 Water contact angle θ (°) Sample Advancing Receding HysteresisBare  29.3 ± 18.2 63.0 ± 7.0 33.7 ± 25.2 fiber Coated 131.4 ± 5.0 114.9± 5.6  16.6 ± 10.6 fiber Control 118.4 ± 0.3 95.8 ± 3.1 22.6 ± 3.3 (flat glass)

Contact angles θ of the bare fibers 10B were in the range of 29-63°indicating the hydrophilic nature of the bare fibers 10B. In contrast,contact angles θ measured on the sealed fiber 10H were in the range of115-131°, indicating that the hermetic sealing layer 50 is hydrophobic.In addition, the contact angle hysteresis of the sealed fibers 10H islower than that for the bare fibers 10B, suggesting good uniformity ofthe hermetic sealing layer 50 on the outer surface 70.

In the case of a silane-based hermetic sealing layer 50, the thicknessTH5 of this layer need not exceed 10 nm. The thickness of a hermeticsealing layer 50 made in the form of a SAM from a silane-based hermeticsealing material 50 m is less than or equal to 10 nm, or less than orequal to 8 nm, or less than or equal to 6 nm, or in the range from 3nm-10 nm, or in the range from 4 nm-8 nm. These ranges for the thicknessTH5 are suitable if the main purpose of the hermetic sealing layer 50 isto provide hydrophobicity. In other embodiments, the hermetic sealinglayer 50 is also used to improve the mechanical properties of the fiberand the thickness TH5 of the hermetic sealing layer 50 is preferablygreater than 10 nm. In an example, the hermetic sealing layer material50 can comprise a fluorosilicone and/or a perfluoroelastomer and thelayer thickness TH5 can be in the range from 10 nm-10 microns, or in therange from 50 nm-5 microns, or in the range from 100 nm-3 microns. Oneexample of the fluorosilicone comprises a polysiloxane backbone with afluorinated pendant groups (e.g. trifluoropropyl groups). Suchfluorosilicones can be moisture cured or catalyst-cured (e.g.platinum-cured) with a hydride crosslinker at room temperature and thecure can be accelerated by applying heat. The fluorosilicones, inaddition to providing hydrophobicity, can also provide shock andvibration absorption and increased durability, thereby increasing themechanical properties of the fibers.

In another example, the hermetic sealing layer material 50M comprises aperfluoroelastomer (FKM). A type of FKM suitable for use as the hermeticsealing layer material 50M is known as VITON®, which is a registeredtrademark of The Chemours Company of Wilmington, Del. In an example, theFKM can be cured by peroxide and can also be grafted with siliconesusing amino-functionalized polydimethyl siloxane. These silicone-graftedFKMs can provide the flexibility of the silicones along with thedurability and tensile strength of the FKMs.

Fiber Ribbon

FIG. 4A is a top-down view of an example optical fiber ribbon (“fiberribbon”) 200 that employs an array 8 of the fibers 10 disclosed herein.FIG. 4B is an x-y cross-sectional view of the example fiber ribbon 200as taken along the line A-A in FIG. 4A. The example fiber ribbon 200 ofFIG. 4A has a substantially constant x-y cross-sectional shape in thez-direction. The array 8 of fibers 10 are arranged in a row i.e., withtheir centerlines AC substantially residing on reference line R1 thatruns in the x-direction (see the close-up inset of FIG. 4B). The fiberribbon 200 has a first end section 201 with a first end 202 and a secondend section 203 with a second end 204.

While the fiber ribbon 200 can generally comprise two or more fibers 10in the fiber array 8, in some preferred embodiments, the fiber ribbon200 comprises multiples of 8 fibers, e.g., 8, 16, 24, etc. In addition,while the fiber ribbon 200 described in detail below includescladding-strengthened optical fibers 10, in other embodiments the fiberribbon 200 may include other types of glass or plastic optical fibers.

The cladding-strengthened optical fibers 10 reside within a commonprotective coating 210, i.e., the common protective coating 210generally surrounds the outer surfaces 70 of the fibers 10. Thecross-sectional view of FIG. 4B shows the fibers 10 encapsulated withinthe common protective coating 210. In some examples, one or both endsections 60 of one or more of the fibers 10 are exposed, as explainedbelow. The common protective coating 210 has an outer surface 221 with atop side 222, a bottom side 224 and edges 226. In an example, the commonprotective coating 210 has an oval, rectangular (with sharp or roundedcorners), or similar elongate shape, with a long dimension LX in thex-direction and a short dimension LY in the y-direction. Note that in anembodiment where the outer surfaces 70 of the fibers 10 are in contactwith each other to maximize the fiber density, the common protectivecoating 210 may not be contact the entire outer surface 70 of each fiber10 at the location where adjacent fibers are in contact. In otherembodiments where the fibers 10 are spaced apart from each other, thecommon protective coating 210 surrounds the entire outer surface 70 ofeach fiber over at least a portion of the length of the fiber ribbon200.

As discussed above, typical optical fibers, in an array or individually,each have an individual protective coating. In contrast, the fibers 10in array 8 do not each include individual protective coatings. Instead,the common protective coating 210 is common to fibers 10 in array 8 offiber ribbon 200. As used herein, a coating is said to be “common” if itis applied to a plurality of fibers 10 of an array 8 and if it makesdirect contact with an outer surface 70 of at least some of theplurality of fibers 10 of the array 8. In some embodiments, for example,the common protective coating directly contacts the outer surface of twoor more of the cladding-strengthened glass optical fibers. The commonprotective coating 210 may be applied simultaneously to the plurality offibers 10 of the array 8. If the plurality of fibers 10 includes two ormore bare fibers 10B, a coating is common if it makes direct contactwith outer surface 32 of at least two of the fibers in the plurality. Ifthe plurality of fibers includes two or more hermetic sealed fibers 10H,a coating is common if it makes direct contact with outer surface 70 ofat least two of the fibers in the plurality.

In an example, the common protective coating 210 is made of a non-glassmaterial, and further in the example is made of a polymer such as thoseused as protective primary or secondary coatings for individual opticalfibers. The polymer is preferably an organic polymer. Such polymersinclude acrylates, methacrylates, and polyamides. Other non-glassmaterials known in the art for coating glass optical fibers can also beused for the common protective coating 210, including thermoplastics andadhesives. In an example, the material used for the common protectivecoating 210 is curable by exposure to ultraviolet (UV) light (i.e., isUV curable). An example thermoplastic has a melt temperature in therange of 160° C. to 260° C., a melt viscosity in the range of 100centipoise (cP) to 10,000 cP, and an operating temperature from −40° C.to 100° C., noting that telecommunications standards involve testingtelecommunications components (including fibers) over a temperaturerange from −40° C. to 85° C.

In an experiment, an example fiber 10 having an outer cladding 30 with athickness of 2 μm was formed using the above-described drawing processusing the drawing system 100 and wound around the take-up spool 150.Then eight fibers 10 were bundled together to form a fiber array 8. Thefiber array 8 was then coated using a thermoplastic split die coatingdrawing process to form a common protective coating 210 around the eightfibers 10. The polymer used to form the common protective coating 210was polyamide (Henkel PA652, also known as MACROMELT OM 652, availablefrom Henkel Corporation, Rocky Hill, Conn.), which was heated to 190° C.as the fiber array 8 passed through. The polyamide coating solidifiedwhen cooled down to less than 120° C. to form the (solid) commonprotective coating 210. With reference to FIG. 4B, the resulting fiberribbon 200 had a dimension LY in the γ-direction 0.21 mm and a dimensionLX in the x-direction of 1.1 mm. The fiber ribbon 200 was measured forbending loss and exhibiting the preferential bending properties asexpected.

FIG. 4C is similar to FIG. 4B and shows an example embodiment whereinthe fibers 10 are arranged in two arrays 8 in the form of rows definedby respective reference lines R1 and R2 that run in the x-direction.More than two rows of fibers 10 can also be implemented, and thediscussion below focuses on a single-row embodiment of the fiber ribbon200 for ease of illustration and explanation.

The fibers 10 define a fiber pitch PR for the fiber ribbon 200, whichdefines the fiber density for the fiber ribbon i.e., the number offibers per unit length along the given row of fibers. As discussedbelow, the fiber pitch PR for the fiber ribbon 200 can be constant withlength along the fiber ribbon, or can change, depending on theparticular fiber ribbon configuration. The fiber pitch PR can be in therange from the fiber diameter DF to 250 microns, wherein the greatestfiber density is about 2× of the greatest fiber density of aconventional fiber ribbon. This factor increases to 4× fortwo-dimensional arrays 8 (i.e., two rows) of fibers 10.

In one embodiment, fiber density is expressed as the separation betweenadjacent glass optical fibers in a fiber ribbon. Each of the fibers in aribbon has a centerline and fiber density is expressed in terms of theseparation between centerlines of adjacent glass optical fibers in thefiber ribbon. The separation of centerlines of adjacent glass opticalfibers is less than 150 microns, or less than 125 microns, or less than100 microns, or less than 80 microns, or less than 60 microns, or in therange from 40 microns-150 microns, or in the range from 60 microns-125microns, or in the range from 75 microns-110 microns.

The fiber density of the fiber ribbon 200 is greater than that of aconventional fiber ribbon mainly because conventional optical fibersinclude individual protective coatings applied during the fiber drawingprocess. Such protective coatings typically have an outer diameter ofabout 240 microns, which approximately doubles the diameter of the fiberrelative to the cladding-strengthened fibers disclosed herein. Withoutthe protective coating, a conventional optical fiber has very highchance of breaking when wound onto the take-up spool because aconventional optical fiber lacks a strengthened outer cladding 32 asdescribed herein, which makes the ribbon fabrication process with highfiber density as disclosed herein impractical to implement. The localstress imparted to a bare glass conventional fiber also presentlong-term reliability risks that are mitigated through inclusion of thestrengthened outer cladding 32.

In one example, the common protective coating 210 is made of a singlepolymer material. In another example illustrated in the close-upcross-sectional view of FIG. 4D, the common protective coating 210includes multiple polymer materials, which in one aspect are layered todefine a primary (inner) layer 212 and a secondary (outer) layer 214 inthe case of two different polymer materials. In an example, thesecondary layer 214 has a higher elastic modulus than the primary layer212, with the elastic modulus of the entire common protective coating210 being an effective elastic modulus that is substantially an averageof the respective elastic moduli of the primary and secondary layers.This configuration provides a relatively soft, cushioning layer closestto the fibers 10 that protects the fibers from mechanical loads whilealso providing a harder, abrasion-resistant layer on the outermostsurface 221 of the fiber ribbon. An example of a dual-layer commonprotective coating 210 that can be effectively utilized to form thefiber ribbon 200 is the Corning® CPC® protective coating, available fromCorning, Inc., Corning, N.Y. In an example, the effective elasticmodulus of a protective coating with one or a plurality of layers is inthe range from 10 MPa-1000 MPa, or in the range from 20 MPa-800 MPa, orin the range from 50 MPa-600 MPa.

The common protective coating 210 may be deposited over the fibers 10using techniques known in the art such as by disposing a curable coatingcomposition on the fibers 10 and then curing the curable coatingcomposition using, for example, ultraviolet (UV) light, heat, or byother means known in the art. In this embodiment, the common protectivecoating 210 is a cured product of the curable coating composition.

The fiber ribbon 200 may optionally include indicia 230, such asgeometrical features, markings, colorings, etc. to identify the polarityof the fiber ribbon. For instance, with reference to FIG. 4E, the commonprotective coating 210 may be made asymmetric relative to the referenceline R1, e.g., the thickness of the common protective coating 210 may bedifferent between the reference line R1 and the top surface 222 ascompared to the thickness between the reference line R1 and the bottomsurface 224. In other example, the top/bottom sides or left/right sidesof the common protective coating 210 can be formed by polymers havingdifferent colors.

Fiber Ribbon Cable

FIG. 5A is a top-down view similar to FIG. 4A and shows an example of afiber ribbon cable 300 formed using the fiber ribbon 200. The fiberribbon cable 300 has first and second end sections 301 and 303 thatrespectively include first and second ends 302 and 304. The first andsecond ends 202 and 204 of the fiber ribbon are shown as coinciding withthe first and second ends 302 and 304 of the fiber ribbon cable, butthis need not be the case.

FIGS. 5B through 5D are cross-sectional views of examples of the fiberribbon cable 300 of FIG. 5A. The fiber ribbon cable 300 includes thefiber ribbon 200 and a cover assembly 310 that surrounds the outersurface 221 of the common protective coating 210 of the fiber ribbon. Inan example, one or more fiber ribbons 200 can be loosely arranged withinthe cover assembly 310, i.e., the fiber ribbon cable 300 can be aloose-buffered cable. In another embodiment, the fiber ribbon cable 300can be a tight-buffered cable.

In the example cover assembly 310 of the fiber ribbon cable of FIG. 5B,the fiber ribbon 200 is surrounded by a strength layer 314 (e.g., aramidyarn), and an outer jacket 320 that surrounds the strength layer. Theexample configuration of FIG. 5C comprises a binder layer 312 thatsurrounds the fiber ribbon 200, with the strength layer 314 surroundingthe binder layer 312 and the outer jacket 320 surrounding the strengthlayer.

FIG. 5D shows an example where the outer jacket 320 is provided directlyto the outer surface 221 of the common protective coating 210 of thefiber ribbon 200.

Various other configurations for the cover assembly 310 as known in theart can also be effectively employed. For example, multiple fiberribbons 200 can supported within the cover assembly 310.

Fiber Ribbon Interconnect

The fiber ribbon 200 is compatible with existing fiber processing toolsand termination components. In one example, a fiber ribbon interconnectis formed by terminating the first and second ends of the fiber ribbon200 with respective optical fiber connectors (“connectors”). In anotherexample, the fiber ribbon interconnect is formed by connectorizing thefiber ribbon at only one end. In another example, a fiber ribboninterconnect includes the cover assembly that forms a fiber ribbon cable300. Most of the example fiber ribbon interconnects discussed below areformed from a fiber ribbon cable 300, but the fiber ribbon interconnectas disclosed herein need not include the cover assembly 310.Furthermore, as noted above, the fiber ribbon interconnect disclosedherein can include only one connectorized end.

Connectorizing the fiber ribbon 200 with connectors to form a fiberribbon interconnect typically requires extracting the fibers 10 from thecommon protective coating 210. This process can be done mechanically,though it may be relatively difficult as compared to conventional fiberribbons. Thus, other stripping approaches, such as chemical strippingand thermal stripping, can be used. An example chemical strippingapproach includes using hot sulfuric acid. An example thermal strippingprocess includes the use of a hot nitrogen jet.

FIG. 6 is an elevated view of an example fiber ribbon interconnect 400that includes the fiber ribbon cable 300 terminated at the first andsecond ends 402 and 404 by respective optical fiber connectors(“connectors”) 450. In an example, the connectors 450 can be the same orsubstantially the same connector. In an example, the one or both of theconnectors 450 can be high-density connectors, denoted 450H. The term“high density” generally means a fiber density that is greater than aconventional optical fiber connector, such as an MPO connector, whichtypically has a fiber density (pitch) of 250 microns. In the discussionbelow, some connectors 450 can be standard-density connectors, and theseare denoted 450S.

High-Density Connector Assembly

FIG. 7A is an exploded front elevated view of an example method offorming a high-density connector assembly (“connector assembly”) 452that can be used directly as the high-density connector 450H or that canbe used to form the high-density connector 450H (e.g., by adding furtherconnector components, as discussed below).

The connector assembly 452 includes a grooved substrate 460 having afront-end section 461 with a front end 462, a back-end section 463 witha back end 464, and a central axis A2 that runs in the z-direction. Thefront-end section 461 has a planar top surface 472 while the back-endsection 463 has a planar top surface 474 that is lower than the topsurface 472 of the front section. The front-end section 461 includes anarray 480 of grooves 482 formed in the planar top surface 472 and thatrun parallel to the central axis A2. In an example, the groovedsubstrate 460 comprises a glass or glass-based material. In an example,the grooves 482 are V-grooves, but other cross-sectional shapes for thegrooves can also be effectively employed.

FIG. 7A shows the end sections 60 of the array 8 of fibers 10 of thefiber ribbon 200 extracted from the common protective coating 210. Thegrooves 480 of the front-end section 461 of the V-groove supportsubstrate 460 are sized to accommodate the end sections 60 of the fibers10 while the back-end section 463 accommodates the fiber ribbon 200,which in an example has been removed from the cover assembly 310 of afiber ribbon cable 300 (e.g., a portion of the cover assembly has beenstripped away). In an example, the fiber pitch P1 at the first end 202of the fiber ribbon 200 is 125 μm and is closely matched to the pitch PVof standard 127 μm grooves 482.

Once the end sections 60 of the fibers 10 are supported in the grooves482, then with reference to FIGS. 7B and 7C, an adhesive 490 is appliedto the fiber ribbon 200 at the back-end section 463. A cover 500 havinga front end 502, a back end 504, a top surface 512 and a bottom surface514 is then placed over the top of the array 480 of grooves 482 tosecure the end sections 60 of the fibers 10 in the front-end section 461of the grooved support substrate 460. The cover 500 is held in place bythe adhesive 490 contacting the back end 504 of the cover. The adhesive490 can also be added to the grooves 482. The cover 500 can be used topress the end sections 60 of the fibers 10 into their respective grooves482. In an example, the cover 500 is a thin planar sheet made of a glassor a glass-based material.

FIG. 7B shows the resulting connector assembly 452, with the end faces62 of the fibers 10 residing substantially at the front end 462 of thegrooved substrate 460. The connector assembly 452 supports the fibers ata pitch P1 (wherein P1=PV), which can be the same as or different thanthe fiber pitch PR of the fiber ribbon 200. The fiber end faces 62 aretypically polished once assembly of the connector assembly 452 iscompleted.

FIG. 7C is y-z cross-sectional view of the connector assembly 452 asattached to the end section 201 of the fiber ribbon 200, which is shownas incorporated into a cover assembly to form a fiber ribbon cable 300.In this case, a portion of the cover assembly 310 is stripped away toexpose the first-end section 201 of the fiber ribbon 200. In an example,the front end 462 of the grooved substrate, the front end 502 of thecover 500 and the end face 62 of the fiber 10 define a tilt angle θrelative to a vertical plane VP to reduce reflection losses. In anexample, the tilt angle θ can be up to about 8 degrees.

FIG. 7D is similar to FIG. 7B and illustrates an example high-densityconnector 450H formed by at least partially enclosing the connectorassembly 452 within a connector housing 454 having a front end 456 and aback end 457. In an example, the high-density connector 450 includes atleast one alignment feature 458, which is shown by way of example asalignment pins that extend from the front end 456 of the connectorhousing to define a plug type connector. The at least one alignmentfeature 458 can also comprise alignment holes sized to receive alignmentpins, thereby defining a receptacle type connector.

The front end 462 of the grooved substrate 460 is shown residing at orproximate to the front end 456 of the connector housing 450 while thefiber ribbon 200 extends from the back end 457 of the connector housing.In another example, the connector assembly 452 can extend from the frontend 456 of the connector housing 454.

Fan-Out Fiber Ribbon

FIG. 8A is a top-down view of an example fiber ribbon 200 similar tothat shown in FIG. 4A, except that the fiber pitch PR is not constantalong the length of the fiber ribbon. FIGS. 8B and 8C arecross-sectional views of the fiber ribbon 200 as taken along the linesB-B and C-C respectively, and show two different fiber pitches PR1 andPR2 as a function of the z-position, and in particular at the front-endsection 201 and the back-end section 203. In an example, the change inthe fiber pitch PR occurs over a fan-out region 250 of length LF, withthe fiber pitch PR1 in the front-end section 201 being substantiallyconstant and the fiber pitch PR2 in the back-end section 203 beingsubstantially constant. The length LF is called the transition length,and the fiber ribbon 200 with the fan-out region 250 is called a fan-outfiber ribbon. In an example, the fiber pitch PR1 at the first end 202 ofthe fiber ribbon 200 is in the range from 80 microns to 125 microns(which can also be the range of the diameter DF of the fiber 10) whilethe fiber pitch PR2 at the second end 204 is greater, such as that for astandard connector, e.g., 250 microns.

The transition length LF of the fan-out region 250 can be designed tominimize the bending stress on the fibers 10. As can be seen in FIG. 8A,the outermost fibers 10 experience the greatest amount of bending, i.e.,the tightest bend radius. In an example, the shape of the fibertransition in the fan-out region 250 is designed to maximize the bendradius along the fiber's path. In one example, the fiber path is a halfperiod of a cosine function, which is also known in the art of waveguidedesign as an “S-bend.” For example, for an 8-fiber fan out, theoutermost fiber 10 has an x position as a function of axial position zas given by x={3.5·(PR2−PR1)/2}·cos{πz/LF}. In an example the transitionlength LF is about 10 mm, so that the minimum bend radius, which occursat both ends of the transition, is at least 46 mm. The correspondingmaximum tensile stress in the fiber 10 at this bend radius is about 14kpsi, which is well within the capability of the fiber.

Reliability research of example fibers 10 showed a significantlyincreased fatigue resistance factor as compared to conventional fibers,even though the tensile strength of the fiber was on par or evenslightly less than conventional fiber. As a result, while conventionalfiber can one operate in the 20%˜30% of proof tested stress level,examples of the fiber 10 are fatigue resistant and can operate at about80% of proof test stress level.

FIG. 9 is a top-down view of an example fiber ribbon assembly 400 thatincludes the fan-out fiber ribbon 200 of FIG. 8A with a high-densityconnector 450H operably attached to the first (narrow) end 202 of thefan-out fiber ribbon and a standard-density connector 450S attached tothe second (wide) end of the fan-out fiber ribbon. In an example, thestandard-density connector 450S comprises an MPO connector that supportsthe fibers 10 at a standard pitch P2 of 250 microns. In an example, thefiber ribbon assembly 400 can include the cover assembly 310, only aportion of which is shown in dashed-line outline in FIG. 9 for ease ofillustration.

Furcated Fiber Ribbon

FIG. 10A is Similar to FIG. 8A and Illustrates an Example Embodiment ofa Furcated fiber ribbon 200 wherein the fiber ribbon is bifurcated at afurcation location 209 into two sub-sections (bifurcations) 200A and200B having respective second ends 204A and 204B and each containing asub-set of the total set (array) of fibers 10. This furcatedconfiguration for the fiber ribbon 200 is useful for example when makingoptical connections to transmitters and receivers that reside onseparate silicon-photonics chips. In other embodiments, there can be twoor more furcations (200A, 200B, 200C, etc.), with the bifurcationembodiment shown by way of example. Also in an example the furcationsneed not have the same number of fibers 10 and need not have the samelength. The furcation location 209 can also be selected for conveniencebased on the given connection application.

FIG. 10B shows cross-sectional views of the example sub-sections 200Aand 200B of the furcated fiber ribbon 200, wherein each sub-sectionincludes four of the eight total fibers 10. In the example furcatedfiber ribbon 200 of FIG. 10B, the first end section 201 of the furcatedfiber ribbon 200 is unfurcated (see also FIG. 8B) and is terminated by asingle connector 450 (e.g., high-density connector 450H) while thesecond end section 203 now comprises two end sections 203A and 203B withrespective ends 204A and 204B each terminated by a connector 450 (e.g.,high-density connectors 450H), as shown in FIG. 10C, to define anexample fiber ribbon interconnect 400. In an example, the furcated fiberribbon 200 can be incorporated into a furcated cover assembly 310 toform a furcated fiber ribbon cable 300.

Optical Data Transmission System

FIG. 11A is a schematic diagram of an example optical data transmissionsystem 700. The optical data transmission system 700 comprises aphotonic device 710 having a circuit board 720 having a top surface 722and that operably supports a photonics chip 730, e.g., asilicon-photonics chip. The photonics chip 730 has a front end 732. Theexample optical data transmission system 700 also includes atelecommunications device 800 having a connector receptacle 810. Theoptical data transmission system 700 also includes an example fiberribbon interconnect 400 with a high-density connector 450H and astandard-density connector 450S.

FIG. 11B is a top-down view of an example photonic device 710. FIG. 11Balso shows the high-density connector 450H at the first end 402 of thefiber ribbon interconnect 400 in position to operably engage thephotonic device. The photonics chip 730 operably supports an array ofoptical waveguides 740. Eight optical waveguides 740 that terminate atthe front end 732 of the photonics chip 730 are shown by way of example.In an example, the optical waveguides 740 comprise channel waveguides.

The photonics chip 730 may be fabricated from any material capable ofhaving optical waveguides 740 disposed thereon or therein. Asnon-limiting examples, the photonics chip 730 may be fabricated from aglass-based material (e.g., glass, glass-ceramic, and fused silica) or asemiconductor material (e.g., silicon). The optical waveguides 740 maybe configured as any known or yet-to-be-developed optical waveguides.Non-limiting example optical waveguides 740 include thin-filmdeposition, photolithographic masking and etching processes, laserwritten waveguides, ion-exchanged waveguides, optical waveguides, amongothers. It will be understood that the optical waveguides 740 may besuitably configured for the operations of the photonics chip 730 and aremerely schematically depicted in a straight-line configuration.

The optical waveguides 740 are operably connected to respective activephotonic elements 750, which in an example can comprise an opticaltransceiver, an optical light source (e.g., a vertical-cavitysurface-emitting laser or VCSEL) or an optical detector. In an example,the photonics chip 730 can comprise a first sub-chip that includes theoptical waveguides 740 and a second sub-chip that includes the activephotonic elements 750.

In an example, the photonics chip 730 is configured to generate and/orreceive optical data signals using the active photonic elements 750 andthe optical waveguides 740. The optical waveguides 740 terminate thefront end 732 of the photonics chip 730. The front end 732 of thephotonics chip 730 can include one or more alignment features 734, whichare shown by way of example as alignment holes. In an example, the front732 and the one or more alignment features 734 define an opticalconnector 760, which is shown by way of example as receptacle type ofoptical connector that complements the plug type of high-densityconnector 450H of the fiber ribbon interconnect 400 and that allows formating and de-mating of the photonic device 710 with the fiber ribboninterconnect to establish optical communication between the opticalwaveguides of the photonics chip 730 and the fibers 10 of the fiberribbon interconnect.

Also shown in FIG. 11B is the connector high-density connector 450having one or more alignment features 458 that are complementary to theone or more alignment features 734 of the photonic device 710. Theexample alignment features 458 are shown in the form of alignment pinssized and configured to closely engage the alignment holes 734 when thehigh-density connector 450 is operably engaged with the photonic device730, as shown in FIG. 11C. The photonic device 710 is shown as havingadditional alignment features 734 that help guide the second connectorinto position relative to the photonics chip 730. The optical waveguides740 have a pitch that matches that of the fibers 10 supported by theconnector 450 so that when the high-density connector 450 is operablyengaged with the photonic device 730, the fibers 10 are in opticalcommunication with respective optical waveguides 740. The opticalwaveguides 740 have a high waveguide density, i.e., greater than thatassociated with standard connectors used in standard optical fibercables.

At the other end of the ribbon interconnect 200, the standard-densityconnector 450S is operably engaged with the connector receptacle 610 ofthe telecommunications device 600. The telecommunications device 600 canbe a wide variety of standard telecommunication devices known in theart, such as a server, a fiber optic cable, an electronics panel in adata center, etc. The standard-density connector 450S has theaforementioned standard fiber density associated with industry standardtelecommunication systems and devices.

With reference to FIG. 11D, in the example where the telecommunicationsdevice 800 is a fiber optic cable 840 terminated by a standard-densityconnector 450S, the connector receptacle 810 can be defined by aconnector adapter 880 having two connector receptacles and used tooperably connect optical fiber cables as is known in the art. Thus, inan example, the ribbon interconnect 400 disclosed herein can be used tooptically connect a photonic device 710 having a high waveguide densityto a remote telecommunications device 800 having a standard fiberdensity.

In another example of the optical data transmission system 700illustrated in FIG. 11E, the ribbon interconnect 400 can be used toestablish optical data communication between one photonic device 710 andanother photonic device.

FIG. 11F is similar to FIG. 11E and shows an example of an optical datatransmission system 700 wherein the fiber ribbon interconnect 500utilizes a bifurcated fiber ribbon 200 to provide high-density opticalinterconnections between one photonic device 710 at the first end 402 ofthe fiber ribbon interconnect 400 and two photonic devices 710 at thesecond ends 404 of the fiber ribbon interconnect.

It will be apparent to those skilled in the art that variousmodifications to the preferred embodiments of the disclosure asdescribed herein can be made without departing from the spirit or scopeof the disclosure as defined in the appended claims. Thus, thedisclosure covers the modifications and variations provided they comewithin the scope of the appended claims and the equivalents thereto.

What is claimed is:
 1. A fiber ribbon, comprising: two or morecladding-strengthened glass optical fibers each having an inner core, anouter cladding, and an outer surface defined by the outer cladding,wherein the outer cladding comprises silica glass; and a commonprotective coating that comprises an organic polymer material thatdirectly contacts the silica glass of the outer surfaces of the two ormore cladding-strengthened glass optical fibers such that the two ormore cladding-strengthened glass optical fibers do not includeindividual protective polymer coatings.
 2. The fiber ribbon according toclaim 1, further comprising: a first optical connector at a first end ofthe fiber ribbon, wherein the first optical connector comprises: agrooved substrate with grooves sized to accommodate end sections of thetwo or more cladding-strengthened glass optical fibers that extend fromthe common protective coating, and a cover for covering the end sectionsof the two or more cladding-strengthened glass optical fibers in thegrooves.
 3. The fiber ribbon according to claim 2, wherein the firstoptical connector further comprises a connector housing that at leastpartially surrounds the grooved substrate and the cover.
 4. The fiberribbon according to claim 1, further comprising a cover assembly that atleast partially surrounds the fiber ribbon.
 5. The fiber ribbonaccording to claim 1, wherein the fiber ribbon comprises a first endsection that includes a first end of the fiber ribbon, a second endsection that includes a second end of the fiber ribbon, and a fan-outregion between the first end section and the second end section.
 6. Thefiber ribbon according to claim 5, wherein the first end section has afirst fiber pitch PR1≤100 μm and the second end section has a secondfiber pitch PR2 of 250 μm or 125 μm.
 7. The fiber ribbon according toclaim 6, wherein the fan-out region has an S-bend configuration andcomprises a transition length LF in the range from about 5 mm to about50 mm.
 8. The fiber ribbon according to claim 1, wherein each of the twoor more cladding-strengthened glass optical fibers contacts at least oneother of the two or more cladding-strengthened glass optical fibers. 9.The fiber ribbon according to claim 1, wherein the organic polymermaterial of the common protective coating directly contacts an entiretyof the outer surface of each cladding-strengthened glass optical fiberof the two or more cladding-strengthened glass optical fibers.
 10. Afiber ribbon, comprising: two or more cladding-strengthened glassoptical fibers each having an inner core, an outer cladding, and anouter surface that is defined by or within 100 nm of the outer cladding,wherein the outer surface comprises an inorganic material; and a commonprotective coating that comprises an organic polymer material thatdirectly contacts the inorganic material of the outer surface of the twoor more cladding-strengthened glass optical fibers such that the two ormore cladding-strengthened glass optical fibers do not includeindividual protective polymer coatings.
 11. The fiber ribbon accordingto claim 10, wherein each cladding-strengthened glass optical fiber ofthe two or more cladding-strengthened glass optical fibers includes ahermetic coating defining the outer surface of the cladding-strengthenedglass optical fiber.
 12. The fiber ribbon according to claim 10, whereinthe outer cladding of each of the two more cladding-strengthened glassoptical fibers defines the outer surface that is directly contacted bythe organic polymer material of the common protective coating.
 13. Thefiber ribbon according to claim 10, wherein each of the two or morecladding-strengthened glass optical fibers contacts at least one otherof the two or more cladding-strengthened glass optical fibers.
 14. Thefiber ribbon according to claim 10, wherein the fiber ribbon comprises afirst end section that includes a first end of the fiber ribbon, asecond end section that includes a second end of the fiber ribbon, and afan-out region between the first end section and the second end section.15. The fiber ribbon according to claim 14, wherein the first endsection has a first fiber pitch PR1≤100 μm and the second end sectionhas a second fiber pitch PR2 of 250 μm or 125 μm.
 16. The fiber ribbonaccording to claim 15, wherein the fan-out region has an S-bendconfiguration and comprises a transition length LF in the range fromabout 5 mm to about 50 mm.
 17. The fiber ribbon according to claim 10,further comprising: a first optical connector at a first end of thefiber ribbon, wherein the first optical connector comprises: a groovedsubstrate with grooves sized to accommodate end sections of the two ormore cladding-strengthened glass optical fibers that extend from thecommon protective coating, and a cover for covering the end sections ofthe two or more cladding-strengthened glass optical fibers in thegrooves.
 18. The fiber ribbon according to claim 17, wherein the firstoptical connector further comprises a connector housing that at leastpartially surrounds the grooved substrate and the cover.